'\" et
.TH DATE "1P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\"
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.\"
.SH NAME
date
\(em write the date and time
.SH SYNOPSIS
.LP
.nf
date \fB[\fR-u\fB] [\fR+\fIformat\fB]\fR
.P
date \fB[\fR-u\fB] \fImmddhhmm\fB[[\fIcc\fB]\fIyy\fB]\fR
.fi
.SH DESCRIPTION
The
.IR date
utility shall write the date and time to standard output
or attempt to set the system date and time.
By default, the current date and time shall be written. If an operand
beginning with
.BR '\(pl' 
is specified, the output format of
.IR date
shall be controlled by the conversion specifications and other text
in the operand.
.SH OPTIONS
The
.IR date
utility shall conform to the Base Definitions volume of POSIX.1\(hy2017,
.IR "Section 12.2" ", " "Utility Syntax Guidelines".
.P
The following option shall be supported:
.IP "\fB\-u\fP" 10
Perform operations as if the
.IR TZ
environment variable was set to the string
.BR \(dqUTC0\(dq ,
or its equivalent historical value of
.BR \(dqGMT0\(dq .
Otherwise,
.IR date
shall use the timezone indicated by the
.IR TZ
environment variable or the system default if that variable is
unset or null.
.SH OPERANDS
The following operands shall be supported:
.IP "+\fIformat\fR" 10
When the format is specified, each conversion specifier shall be
replaced in the standard output by its corresponding value. All other
characters shall be copied to the output without change. The output
shall always be terminated with a
<newline>.
.SS "Conversion Specifications"
.RS 10 
.IP "\fR%a\fR" 8
Locale's abbreviated weekday name.
.IP "\fR%A\fR" 8
Locale's full weekday name.
.IP "\fR%b\fR" 8
Locale's abbreviated month name.
.IP "\fR%B\fR" 8
Locale's full month name.
.IP "\fR%c\fR" 8
Locale's appropriate date and time representation.
.IP "\fR%C\fR" 8
Century (a year divided by 100 and truncated to an integer) as a
decimal number [00,99].
.IP "\fR%d\fR" 8
Day of the month as a decimal number [01,31].
.IP "\fR%D\fR" 8
Date in the format \fImm\fP/\fIdd\fP/\fIyy\fR.
.IP "\fR%e\fR" 8
Day of the month as a decimal number [1,31] in a two-digit field
with leading
<space>
character fill.
.IP "\fR%h\fR" 8
A synonym for
.BR %b .
.IP "\fR%H\fR" 8
Hour (24-hour clock) as a decimal number [00,23].
.IP "\fR%I\fR" 8
Hour (12-hour clock) as a decimal number [01,12].
.IP "\fR%j\fR" 8
Day of the year as a decimal number [001,366].
.IP "\fR%m\fR" 8
Month as a decimal number [01,12].
.IP "\fR%M\fR" 8
Minute as a decimal number [00,59].
.IP "\fR%n\fR" 8
A
<newline>.
.IP "\fR%p\fR" 8
Locale's equivalent of either AM or PM.
.IP "\fR%r\fR" 8
12-hour clock time [01,12] using the AM/PM notation; in the POSIX
locale, this shall be equivalent to
.BR %I :\c
.BR %M :\c
.BR %S
.BR %p .
.IP "\fR%S\fR" 8
Seconds as a decimal number [00,60].
.IP "\fR%t\fR" 8
A
<tab>.
.IP "\fR%T\fR" 8
24-hour clock time [00,23] in the format \fIHH\fP:\fIMM\fP:\fISS\fP.
.IP "\fR%u\fR" 8
Weekday as a decimal number [1,7] (1=Monday).
.IP "\fR%U\fR" 8
Week of the year (Sunday as the first day of the week) as a decimal
number [00,53]. All days in a new year preceding the first Sunday
shall be considered to be in week 0.
.IP "\fR%V\fR" 8
Week of the year (Monday as the first day of the week) as a decimal
number [01,53]. If the week containing January 1 has four or more
days in the new year, then it shall be considered week 1; otherwise, it
shall be the last week of the previous year, and the next week shall be
week 1.
.IP "\fR%w\fR" 8
Weekday as a decimal number [0,6] (0=Sunday).
.IP "\fR%W\fR" 8
Week of the year (Monday as the first day of the week) as a decimal
number [00,53]. All days in a new year preceding the first Monday
shall be considered to be in week 0.
.IP "\fR%x\fR" 8
Locale's appropriate date representation.
.IP "\fR%X\fR" 8
Locale's appropriate time representation.
.IP "\fR%y\fR" 8
Year within century [00,99].
.IP "\fR%Y\fR" 8
Year with century as a decimal number.
.IP "\fR%Z\fR" 8
Timezone name, or no characters if no timezone is determinable.
.IP "\fR%%\fR" 8
A
<percent-sign>
character.
.P
See the Base Definitions volume of POSIX.1\(hy2017,
.IR "Section 7.3.5" ", " "LC_TIME"
for the conversion specifier values in the POSIX locale.
.SS "Modified Conversion Specifications"
.P
Some conversion specifiers can be modified by the
.BR E
and
.BR O
modifier characters to indicate a different format or specification as
specified in the
.IR LC_TIME
locale description (see the Base Definitions volume of POSIX.1\(hy2017,
.IR "Section 7.3.5" ", " "LC_TIME").
If the corresponding keyword (see
.BR era ,
.BR era_year ,
.BR era_d_fmt ,
and
.BR alt_digits
in the Base Definitions volume of POSIX.1\(hy2017,
.IR "Section 7.3.5" ", " "LC_TIME")
is not specified or not supported for the current locale,
the unmodified conversion specifier value shall be used.
.IP "\fR%Ec\fR" 8
Locale's alternative appropriate date and time representation.
.IP "\fR%EC\fR" 8
The name of the base year (period) in the locale's alternative
representation.
.IP "\fR%Ex\fR" 8
Locale's alternative date representation.
.IP "\fR%EX\fR" 8
Locale's alternative time representation.
.IP "\fR%Ey\fR" 8
Offset from
.BR %EC
(year only) in the locale's alternative representation.
.IP "\fR%EY\fR" 8
Full alternative year representation.
.IP "\fR%Od\fR" 8
Day of month using the locale's alternative numeric symbols.
.IP "\fR%Oe\fR" 8
Day of month using the locale's alternative numeric symbols.
.IP "\fR%OH\fR" 8
Hour (24-hour clock) using the locale's alternative numeric symbols.
.IP "\fR%OI\fR" 8
Hour (12-hour clock) using the locale's alternative numeric symbols.
.IP "\fR%Om\fR" 8
Month using the locale's alternative numeric symbols.
.IP "\fR%OM\fR" 8
Minutes using the locale's alternative numeric symbols.
.IP "\fR%OS\fR" 8
Seconds using the locale's alternative numeric symbols.
.IP "\fR%Ou\fR" 8
Weekday as a number in the locale's alternative representation (Monday
= 1).
.IP "\fR%OU\fR" 8
Week number of the year (Sunday as the first day of the week) using the
locale's alternative numeric symbols.
.IP "\fR%OV\fR" 8
Week number of the year (Monday as the first day of the week, rules
corresponding to
.BR %V ),
using the locale's alternative numeric symbols.
.IP "\fR%Ow\fR" 8
Weekday as a number in the locale's alternative representation (Sunday
= 0).
.IP "\fR%OW\fR" 8
Week number of the year (Monday as the first day of the week) using the
locale's alternative numeric symbols.
.IP "\fR%Oy\fR" 8
Year (offset from
.BR %C )
in alternative representation.
.RE
.IP "\fImmddhhmm\fB[[\fIcc\fB]\fIyy\fB]\fR" 10
.br
Attempt to set the system date and time from the value given in the
operand. This is only possible if the user has appropriate privileges
and the system permits the setting of the system date and time. The
first
.IR mm
is the month (number);
.IR dd
is the day (number);
.IR hh
is the hour (number, 24-hour system); the second
.IR mm
is the minute (number);
.IR cc
is the century and is the first two digits of the year (this is
optional);
.IR yy
is the last two digits of the year and is optional. If century is not
specified, then values in the range [69,99] shall refer to years
1969 to 1999 inclusive, and values in the range [00,68] shall refer
to years 2000 to 2068 inclusive. The current year is the default if
.IR yy
is omitted.
.RS 10 
.TP 10
.BR Note:
It is expected that in a future version of this standard the default
century inferred from a 2-digit year will change. (This would apply
to all commands accepting a 2-digit year as input.)
.P
.RE
.SH STDIN
Not used.
.SH "INPUT FILES"
None.
.SH "ENVIRONMENT VARIABLES"
The following environment variables shall affect the execution of
.IR date :
.IP "\fILANG\fP" 10
Provide a default value for the internationalization variables that are
unset or null. (See the Base Definitions volume of POSIX.1\(hy2017,
.IR "Section 8.2" ", " "Internationalization Variables"
for the precedence of internationalization variables used to determine
the values of locale categories.)
.IP "\fILC_ALL\fP" 10
If set to a non-empty string value, override the values of all the
other internationalization variables.
.IP "\fILC_CTYPE\fP" 10
Determine the locale for the interpretation of sequences of bytes of
text data as characters (for example, single-byte as opposed to
multi-byte characters in arguments).
.IP "\fILC_MESSAGES\fP" 10
.br
Determine the locale that should be used to affect the format and
contents of diagnostic messages written to standard error.
.IP "\fILC_TIME\fP" 10
Determine the format and contents of date and time strings written by
.IR date .
.IP "\fINLSPATH\fP" 10
Determine the location of message catalogs for the processing of
.IR LC_MESSAGES .
.IP "\fITZ\fP" 10
Determine the timezone in which the time and date are written, unless
the
.BR \-u
option is specified. If the
.IR TZ
variable is unset or null and
.BR \-u
is not specified, an unspecified system default timezone is used.
.SH "ASYNCHRONOUS EVENTS"
Default.
.SH STDOUT
When no formatting operand is specified, the output in the POSIX locale
shall be equivalent to specifying:
.sp
.RS 4
.nf

date "+%a %b %e %H:%M:%S %Z %Y"
.fi
.P
.RE
.SH STDERR
The standard error shall be used only for diagnostic messages.
.SH "OUTPUT FILES"
None.
.SH "EXTENDED DESCRIPTION"
None.
.SH "EXIT STATUS"
The following exit values shall be returned:
.IP "\00" 6
The date was written successfully.
.IP >0 6
An error occurred.
.SH "CONSEQUENCES OF ERRORS"
Default.
.LP
.IR "The following sections are informative."
.SH "APPLICATION USAGE"
Conversion specifiers are of unspecified format when not in the POSIX
locale. Some of them can contain
<newline>
characters in some locales, so it may be difficult to use the format
shown in standard output for parsing the output of
.IR date
in those locales.
.P
The range of values for
.BR %S
extends from 0 to 60 seconds to accommodate the occasional leap second.
.P
Although certain of the conversion specifiers in the POSIX locale (such
as the name of the month) are shown with initial capital letters, this
need not be the case in other locales. Programs using these fields may
need to adjust the capitalization if the output is going to be used at
the beginning of a sentence.
.P
The date string formatting capabilities are intended for use in
Gregorian-style calendars, possibly with a different starting year (or
years). The
.BR %x
and
.BR %c
conversion specifications, however, are intended for local
representation; these may be based on a different, non-Gregorian
calendar.
.P
The
.BR %C
conversion specification was introduced to allow a fallback for the
.BR %EC
(alternative year format base year); it can be viewed as the base of
the current subdivision in the Gregorian calendar. The century number
is calculated as the year divided by 100 and truncated to an integer;
it should not be confused with the use of ordinal numbers for centuries
(for example, ``twenty-first century''.) Both the
.BR %Ey
and
.BR %y
can then be viewed as the offset from
.BR %EC
and
.BR %C ,
respectively.
.P
The
.BR E
and
.BR O
modifiers modify the traditional conversion specifiers, so that they
can always be used, even if the implementation (or the current locale)
does not support the modifier.
.P
The
.BR E
modifier supports alternative date formats, such as the Japanese
Emperor's Era, as long as these are based on the Gregorian calendar
system. Extending the
.BR E
modifiers to other date elements may provide an implementation-defined
extension capable of supporting other calendar systems, especially in
combination with the
.BR O
modifier.
.P
The
.BR O
modifier supports time and date formats using the locale's alternative
numerical symbols, such as Kanji or Hindi digits or ordinal number
representation.
.P
Non-European locales, whether they use Latin digits in computational
items or not, often have local forms of the digits for use in date
formats. This is not totally unknown even in Europe; a variant of dates
uses Roman numerals for the months: the third day of September 1991
would be written as 3.IX.1991. In Japan, Kanji digits are regularly
used for dates; in Arabic-speaking countries, Hindi digits are used.
The
.BR %d ,
.BR %e ,
.BR %H ,
.BR %I ,
.BR %m ,
.BR %S ,
.BR %U ,
.BR %w ,
.BR %W ,
and
.BR %y
conversion specifications always return the date and time field in
Latin digits (that is, 0 to 9). The
.BR %O
modifier was introduced to support the use for display purposes of
non-Latin digits. In the
.IR LC_TIME
category in
.IR localedef ,
the optional
.BR alt_digits
keyword is intended for this purpose. As an example, assume the
following (partial)
.IR localedef
source:
.sp
.RS 4
.nf

alt_digits  "";"I";"II";"III";"IV";"V";"VI";"VII";"VIII" \e
            "IX";"X";"XI";"XII"
d_fmt       "%e.%Om.%Y"
.fi
.P
.RE
.P
With the above date, the command:
.sp
.RS 4
.nf

date "+%x"
.fi
.P
.RE
.P
would yield 3.IX.1991. With the same
.BR d_fmt ,
but without the
.BR alt_digits ,
the command would yield 3.9.1991.
.SH EXAMPLES
.IP " 1." 4
The following are input/output examples of
.IR date
used at arbitrary times in the POSIX locale:
.RS 4 
.sp
.RS 4
.nf

\fB$ \fRdate
\fBTue Jun 26 09:58:10 PDT 1990
.P
\fB$ \fRdate "+DATE: %m/%d/%y%nTIME: %H:%M:%S"
\fBDATE: 11/02/91
\fBTIME: 13:36:16
.P
\fB$ \fRdate "+TIME: %r"
\fBTIME: 01:36:32 PM\fR
.fi
.P
.RE
.RE
.IP " 2." 4
Examples for Denmark, where the default date and time format is
.BR %a
.BR %d
.BR %b
.BR %Y
.BR %T
.BR %Z :
.RS 4 
.sp
.RS 4
.nf

\fB$ \fRLANG=da_DK.iso_8859-1 date
\fBons 02 okt 1991 15:03:32 CET
.P
\fB$ \fRLANG=da_DK.iso_8859-1 \e
    date "+DATO: %A den %e. %B %Y%nKLOKKEN: %H:%M:%S"
\fBDATO: onsdag den 2. oktober 1991
\fBKLOKKEN: 15:03:56\fR
.fi
.P
.RE
.RE
.IP " 3." 4
Examples for Germany, where the default date and time format is
.BR %a
.BR %d .\c
.BR %h .\c
.BR %Y ,
.BR %T
.BR %Z :
.RS 4 
.sp
.RS 4
.nf

\fB$ \fRLANG=De_DE.88591 date
\fBMi 02.Okt.1991, 15:01:21 MEZ
.P
\fB$ \fRLANG=De_DE.88591 date "+DATUM: %A, %d. %B %Y%nZEIT: %H:%M:%S"
\fBDATUM: Mittwoch, 02. Oktober 1991
\fBZEIT: 15:02:02\fR
.fi
.P
.RE
.RE
.IP " 4." 4
Examples for France, where the default date and time format is
.BR %a
.BR %d
.BR %h
.BR %Y
.BR %Z
.BR %T :
.RS 4 
.sp
.RS 4
.nf

\fB$ \fRLANG=Fr_FR.88591 date
\fBMer 02 oct 1991 MET 15:03:32
.P
\fB$ \fRLANG=Fr_FR.88591 date "+JOUR: %A %d %B %Y%nHEURE: %H:%M:%S"
\fBJOUR: Mercredi 02 octobre 1991
\fBHEURE: 15:03:56\fR
.fi
.P
.RE
.RE
.SH RATIONALE
Some of the new options for formatting are from the ISO\ C standard. The
.BR \-u
option was introduced to allow portable access to Coordinated Universal
Time (UTC).
The string
.BR \(dqGMT0\(dq 
is allowed as an equivalent
.IR TZ
value to be compatible with all of the systems using the BSD
implementation, where this option originated.
.P
The
.BR %e
format conversion specification (adopted from System V) was added
because the ISO\ C standard conversion specifications did not provide any way to
produce the historical default
.IR date
output during the first nine days of any month.
.P
There are two varieties of day and week numbering supported (in
addition to any others created with the locale-dependent
.BR %E
and
.BR %O
modifier characters):
.IP " *" 4
The historical variety in which Sunday is the first day of the week and
the weekdays preceding the first Sunday of the year are considered week
0. These are represented by
.BR %w
and
.BR %U .
A variant of this is
.BR %W ,
using Monday as the first day of the week, but still referring to week
0. This view of the calendar was retained because so many historical
applications depend on it and the ISO\ C standard
\fIstrftime\fR()
function, on which many
.IR date
implementations are based, was defined in this way.
.IP " *" 4
The international standard, based on the ISO\ 8601:\|2004 standard where Monday is the
first weekday and the algorithm for the first week number is more
complex: If the week (Monday to Sunday) containing January 1 has four
or more days in the new year, then it is week 1; otherwise, it is week
53 of the previous year, and the next week is week 1. These are
represented by the new conversion specifications
.BR %u
and
.BR %V ,
added as a result of international comments.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
The Base Definitions volume of POSIX.1\(hy2017,
.IR "Section 7.3.5" ", " "LC_TIME",
.IR "Chapter 8" ", " "Environment Variables",
.IR "Section 12.2" ", " "Utility Syntax Guidelines"
.P
The System Interfaces volume of POSIX.1\(hy2017,
.IR "\fIfprintf\fR\^(\|)",
.IR "\fIstrftime\fR\^(\|)"
.\"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
.PP
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
